#include <bits/stdc++.h>
using namespace std;
char grid[4000][4000];
int dist[4000][4000];
vector<pair<int, int>> dirs = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
int main() {
int h, w; cin >> h >> w;
for(int i = 0; i < h; ++i) {
for(int j = 0; j < w; ++j) {
cin >> grid[i][j];
}
}
function<bool(int, int)> valid = [&](int y, int x) {
return (y >= 0 && y < h && x >= 0 && x < w);
};
int ans = 0;
deque<pair<int, int>> q;
q.push_front({0, 0});
dist[0][0] = 1;
while(!q.empty()) {
int y = q.front().first, x = q.front().second;
q.pop_front();
ans = max(ans, dist[y][x]);
for(auto dir : dirs) {
int dy = y + dir.first;
int dx = x + dir.second;
if(!valid(dy, dx)) continue;
if(dist[dy][dx] != 0 || grid[dy][dx] == '.') continue;
if(grid[dy][dx] != grid[y][x]) {
dist[dy][dx] = dist[y][x] + 1;
q.push_back({dy, dx});
} else {
dist[dy][dx] = dist[y][x];
q.push_front({dy, dx});
}
}
}
cout << ans << "\n";
}
